1. Field of the Invention
The present invention relates to an endoscope system.
2. Description of the Related Art
In an endoscope system widely used, light emitted from a lamp provided in a light source device is guided by a light guide provided along an endoscope inserting section, and illumination light thus guided by the light guide is emitted through an illumination window disposed at a tip of the endoscope inserting section for irradiating an examination target site. On the contrary, a laser light source is used instead of the lamp for the illumination in some endoscope systems. For example, in a lighting apparatus described in JP 2005-205195 A, light emitted from a blue semiconductor laser is guided to a tip of an endoscope inserting section through an optical fiber for exciting a phosphor disposed at a tip of the optical fiber to emit light, so that white illumination light thus obtained illuminates an examination target site. This lighting apparatus may attain both the required narrowness of the light guide of the endoscope and the brightness of the illumination light.
It is known, however, that intensity noises such as a hopping mode noise, a return light noise and a speckle noise on an irradiated face are caused in using a semiconductor laser. As described in JP 2005-205195 A, when a semiconductor laser is used, such a phenomenon occurs that a noise pattern in the form of spots fluctuation on an irradiated face depending on an irregular shape of the irradiated face. This fine fluctuation is caused due to speckle interference. Since such fine fluctuation may be an obstacle to observation of a diseased part when the illumination light is used in an endoscope or the like, a technique to prevent the fluctuation is now being studied.